Lower aliphatic amines find applications as organic intermediates for the synthesis of drugs, but also as bactericides, herbicides, rubber accelerators, corrosion inhibitors, extraction agents in the production of penicillin, surface active agents, etc.
Previously morpholine has been used as a rubber accelerator in various processes. Recently in the art there has been a trend to use primary amines as alternatives for morpholine. It has been demonstrated that highly hindered primary amines such as t-butylamine are especially useful in this regard.
Methods of preparation of primary amines are known in the art. "Functionalisation of Alkenes: Catalytic Amination of Monoolefins", by J. J. Brunet et al., J. Mol. Catal., 49 (1989) 235-259 presents a review of amination of monoolefins.
The most widespread method for producing lower aliphatic amines is a reaction first achieved by Sabatier, involving the reaction of ammonia and an alcohol. Catalysts which have been used for the Sabatier reaction include silica-alumina, binary transition metal oxides, various metal phosphates and, recently, zeolites. Processes involving the reaction of ammonia and alcohols produce water which has to be separated from the product amine. It would be very desirable in the art if amines could be manufactured directly from alkenes, because it would save at least one-step in commercial operations. However, the conclusion of this article is that no expedient process has emerged for the catalytic amination of alkenes with ammonia or amines except for reactions with ethylene.
The direct addition of ammonia to alkenes is thermodynamically feasible, at least for ethylene and propylene, and can be accomplished in two ways, either by activation of the olefinic bond by coordination on a metal complex, thus forming a new species which can undergo nucleophilic attack by activation of the amine, or by activation of the amine by making it either more electrophilic (via amino radicals) or more nucleophilic (via metal amides).
Activation of an olefin can be promoted by many transition metals, however generally none of the products are the result of a simple monoaddition of the nucleophile on the olefin.
Organic and inorganic derivatives of Pd, Pt, Rh, Ru, Os or Ir, preferably on a support such as Al.sub.2 O.sub.3, have been used to add ammonia to C.sub.2 -C.sub.6 alkenes, however the conversions and selectivities were apparently low (see U.S. Pat. No. 3,412,158).
The addition of secondary aliphatic amines, including dimethylamine, methylamine, n-butylethylamine, pyrrolidine, morpholine and piperidine to ethylene in the presence of homogeneous Rh- or Ir- based catalysts to produce tertiary amines was reported by D. R. Coulson in the early 70s, see U.S. Pat. No. 3,758,586. Primary amines and ammonia did not react with ethylene under these conditions.
Catalytic amination of alkenes with ruthenium or iron catalysts was disclosed in European Patent Application 39061 (1981) to D. M. Gardner and R. T. Clark, as well as in U.S. Pat. No. 4,454,321 (1984). Here, reasonable conversions and yields appear to be limited to the use of ethylene as the alkene.
Markovnikov-addition-type monoamines have been formed by vapor phase amination of monoolefins in the presence of alumino silicates, see U.S. Pat. No. 4,307,250 (1981) and U.S. Pat. No. 4,375,002 (1983) to J. O. H. Peterson et al. Highest activities were obtained with small to medium pore acidic zeolites such as H-eronite and H-clinoptilotite, which were more effective than standard Linde SK-500 zeolite, a rare earth-exchanged Y zeolite. In addition, these catalysts exhibit higher life at high temperature, thus decreasing the chance of ethylene polymerization and other side reactions. Further, stoichiometric excess of ammonia appeared to contribute to high selectivities to monoethylamine.
Similar zeolite catalysts have been used by others to effect ethylene amination to ethylamine. An article titled "Direct Amination of Ethylene by Zeolite Catalysis" by M. Deeba, M. E. Ford and T. A. Johnson, J. Chem. Soc. Commun., 1987, 562, describes the formation of ethylamine by addition of ammonia to ethylene catalyzed by acidic zeolites such as H-Y, H-mordenite and H-erionite.
The characteristic which allows these zeolites to act as catalysts for ethylene amination results from the highly acidic nature of the proton-exchanged zeolites. The necessity of strongly acidic sites and, thus, of a protonated ethylene intermediate for catalytic amination is demonstrated by the negligible activity of the non-acidic, sodium ion-exchanged, offretite and Y-zeolites and the weakly acidic amorphous silica alumina. Again, a high selectivity was observed and was believed to be the result of a stoichiometric excess of ammonia, Ibid.
The same researchers reported further work in "Amination of Olefins by Zeolites" by Deeba et al., Catalysis, 1987, 221. H-offretite, H-erionite, H-clinoptilolite, H-Y, and rare earth-exchanged Y were employed to obtain selectivities to the corresponding amines as high as 97%. This work included the conversions of ethylene, propylene and isobutylene to the corresponding amines.
Isobutylene was selectively converted to isobutylamine with greater than 98% yield between 220.degree. C. and 300.degree. C. It was noted that there was no detectable conversion of isobutylene with small pore zeolites such as H-erionite or H-clinoptilolite.
The activity of the zeolites investigated was correlated to the number of strong acid sites as determined by ammonia TPD.
It is also indicated that the mechanism of olefin amination results from the high acidic nature of proton-exchanged zeolites, wherein ethylene and propylene are reversibly adsorbed by zeolites, probably by means of the formation of a pi complex between the surface hydroxy group and the olefin.
It was also concluded that conversion of ethylene required the highest temperatures and the strongest acid sites, while propylene formed a more stable cationic intermediate activated by somewhat weaker acid sites.
In the case of isobutylene amination by ammonia, calculated product distributions indicate amination is favored by low temperature, high pressure and high ammonia/isobutylene ratios. Deeba et al. also noted that the activity of the solid acid catalysts generally correlates with the number of strong acid sites, and that t-butylamine formation likely involves the formation of the tert-butyl cation (see "Heterogeneous Acid-Catalyzed Amination of Isobutene to tert-Butylamine", J. Org Chem., 1988, 53, 4594-4596).
Modified zeolites have also been used for producing amines. In German Patent 3327-000A to BASF borosilicate or borogermanate zeolite catalysts were used for amine production.
In German Patent 3634-247C to BASF chromium-containing borosilicate or ferrosilicate zeolite catalysts were used.
Zeolite catalysts were also used for preparation of amines by V. Taglieber et al., Canadian Patent 1,218,677 (1987) to BASF. In this process ammonia and amines are mixed with the olefin and reacted from about 200 to 300 bar and about 250.degree. to 350.degree. C. The catalysts are zeolites of the pentasil type.
Furthermore, U.S. Pat. No. 4,302,603 (1981), to G. Pez, discloses that a substantial improvement is obtained when the direct reaction of a monoolefin with ammonia is homogeneously catalyzed in liquid ammonia by CsNH.sub.2, RbNH.sub.2 or mixtures which may also include KNH.sub.2 or NaNH.sub.2 at temperatures below the critical temperature of ammonia.
U.S. Pat. No. 4,483,757 (1984) to Gardner et al., discloses the use of light energy in the presence of specified ammonium halides, such as NH.sub.4 I or bromide, as photopromoters for the addition of ammonia, primary or secondary amines to C.sub.2 -C.sub.18 monoolefinic compounds. The cost of such a process would be prohibitively expensive for large scale production.
It is also known in the art to produce t-butylamine by Ritter Chemistry wherein isobutylene is reacted with HCN to produce butylformamide which is hydrolyzed to t-butylamine plus formic acid. However, the use of HCN is very hazardous.
It would be a distinct advance in the art if there were discovered a very active, long life catalyst for preparation of alkylamines by addition of ammonia to olefins which were less expensive than any discussed which have been used in the art. It would be especially desirable if the catalyst allowed for the continuous synthesis of t-butylamine at the thermodynamically calculated limit of isobutylene conversion. As mentioned isobutylamine is being used more often as a substitute for morpholine as a rubber accelerator and improved methods of preparation are of importance to those in the art.